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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Valid Parenthesis String - LeetCode 678</title>
<link rel="stylesheet" href="styles.css">
<script src="https://d3js.org/d3.v7.min.js"></script>
</head>
<body>
<div class="container">
<div class="problem-info">
<h1><span class="problem-number">#0678</span> Valid Parenthesis String</h1>
<p><strong>Problem:</strong> Check if string with '(', ')', '*' can be valid. '*' can be '(', ')' or empty.</p>
<p><strong>Pattern:</strong> Greedy with Range - Track min/max possible open count</p>
<div class="problem-meta">
<span class="meta-tag">🔤 String</span>
<span class="meta-tag">📚 Stack</span>
<span class="meta-tag">⏱️ O(n)</span>
</div>
<div class="file-ref">
📄 Python: <code>python/0678_valid_parenthesis_string/0678_valid_parenthesis_string.py</code>
</div>
</div>
<div class="explanation-panel">
<h4>🧠 How It Works (Layman's Terms)</h4>
<p>A stack works like a <strong>pile of plates</strong> - last in, first out (LIFO):</p>
<ul>
<li><strong>Push:</strong> Add item to the top</li>
<li><strong>Pop:</strong> Remove and return the top item</li>
<li><strong>Peek:</strong> Look at top without removing</li>
<li><strong>Match pairs:</strong> Great for matching brackets, parentheses</li>
</ul>
</div>
<div class="visualization-section">
<h3>🎬 Step-by-Step Visualization</h3>
<div class="visualization">
<svg id="mainSvg"></svg>
</div>
<div class="controls">
<button id="stepBtn">Step</button>
<button id="autoBtn">Auto Run</button>
<button id="resetBtn">Reset</button>
<div class="speed-control">
<label for="speed">Speed:</label>
<input type="range" id="speed" min="100" max="2000" value="800">
</div>
</div>
<div class="status" id="status">Click "Step" to validate string</div>
<div class="variables">
<div class="var-item">
<span class="var-label">Input:</span>
<span id="inputDisplay">"(*)"</span>
</div>
<div class="var-item">
<span class="var-label">Open Range (min, max):</span>
<span id="rangeDisplay">(0, 0)</span>
</div>
<div class="var-item">
<span class="var-label">Valid:</span>
<span id="resultDisplay">-</span>
</div>
</div>
</div>
<div class="code-section">
<h3>💻 Python Solution</h3>
<div class="code-block">
<pre>from typing import List, Optional
"""
LeetCode Valid Parenthesis String
Problem from LeetCode: https://leetcode.com/problems/valid-parenthesis-string/
Description:
Given a string s containing only three types of characters: '(', ')' and '*', return true if s is valid.
The following rules define a valid string:
1. Any left parenthesis '(' must have a corresponding right parenthesis ')'.
2. Any right parenthesis ')' must have a corresponding left parenthesis '('.
3. Left parenthesis '(' must go before the corresponding right parenthesis ')'.
4. '*' could be treated as a single right parenthesis ')' or a single left parenthesis '(' or an empty string "".
Example 1:
Input: s = "()"
Output: true
Example 2:
Input: s = "(*)"
Output: true
Example 3:
Input: s = "(*))"
Output: true
Constraints:
1 <= s.length <= 100
s consists of characters '(', ')' and '*'.
"""
class Solution:
def check_valid_string(self, s: str) ->bool:
"""
Determine if the input string is valid.
An input string is valid if:
1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.
3. '*' could be treated as a single right parenthesis ')' or a single left parenthesis '(' or an empty string "".
Args:
s: The input string containing only '(', ')' and '*'
Returns:
bool: True if the string is valid, False otherwise
"""
min_open = 0
max_open = 0
for char in s:
if char == '(':
min_open += 1
max_open += 1
elif char == ')':
min_open -= 1
max_open -= 1
else:
min_open -= 1
max_open += 1
if max_open < 0:
return False
min_open = max(min_open, 0)
return min_open == 0
def checkValidString_dp(self, s: str) ->bool:
"""
Alternative implementation using dynamic programming.
Args:
s: The input string containing only '(', ')' and '*'
Returns:
bool: True if the string is valid, False otherwise
"""
n = len(s)
if n == 0:
return True
dp = [([False] * n) for _ in range(n)]
for i in range(n):
if s[i] == '*':
dp[i][i] = True
for i in range(n - 1):
if (s[i] == '(' or s[i] == '*') and (s[i + 1] == ')' or s[i + 1
] == '*'):
dp[i][i + 1] = True
for length in range(3, n + 1):
for i in range(n - length + 1):
j = i + length - 1
if s[i] == '*' and dp[i + 1][j]:
dp[i][j] = True
continue
if (s[i] == '(' or s[i] == '*') and (s[j] == ')' or s[j] == '*'
):
if j - i == 1 or dp[i + 1][j - 1]:
dp[i][j] = True
continue
for k in range(i, j):
if dp[i][k] and dp[k + 1][j]:
dp[i][j] = True
break
return dp[0][n - 1]
def checkValidString_greedy(self, s: str) ->bool:
"""
Greedy approach with two passes to check for validity.
Args:
s: The input string containing only '(', ')' and '*'
Returns:
bool: True if the string is valid, False otherwise
"""
balance = 0
for char in s:
if char == '(' or char == '*':
balance += 1
else:
balance -= 1
if balance < 0:
return False
if balance == 0:
return True
balance = 0
for char in reversed(s):
if char == ')' or char == '*':
balance += 1
else:
balance -= 1
if balance < 0:
return False
return True
if __name__ == '__main__':
# Example usage based on LeetCode sample
solution = Solution()
# Example 1
s1 = "()"
result1 = solution.check_valid_string(s1)
print(f"Example 1: {result1}") # Expected: True
# Example 2
s2 = "(*)"
result2 = solution.check_valid_string(s2)
print(f"Example 2: {result2}") # Expected: True
# Example 3
s3 = "(*))"
result3 = solution.check_valid_string(s3)
print(f"Example 3: {result3}") # Expected: True
# Test with DP approach
print("\nWith DP approach:")
result4 = solution.checkValidString_dp(s3)
print(f"Example 3: {result4}") # Expected: True
# Test with greedy approach
print("\nWith greedy approach:")
result5 = solution.checkValidString_greedy(s3)
print(f"Example 3: {result5}") # Expected: True
</pre>
</div>
</div>
</div>
<script>
const s = "(*)";
let idx = 0;
let minOpen = 0, maxOpen = 0;
let isValid = null;
let autoRunning = false;
let autoTimer = null;
const width = 700;
const height = 400;
const svg = d3.select("#mainSvg")
.attr("width", width)
.attr("height", height);
const charWidth = 70;
const startX = (width - s.length * charWidth) / 2;
function draw() {
svg.selectAll("*").remove();
svg.append("text")
.attr("x", width / 2).attr("y", 25)
.attr("text-anchor", "middle")
.attr("font-weight", "bold")
.text(`Validating: "${s}"`);
// Draw string
for (let i = 0; i < s.length; i++) {
const x = startX + i * charWidth + charWidth / 2;
const y = 100;
let fill = "#e3f2fd", stroke = "#1976d2";
if (i < idx) {
fill = "#e0e0e0"; stroke = "#757575";
} else if (i === idx) {
fill = "#ffeb3b"; stroke = "#f57c00";
}
svg.append("rect")
.attr("x", x - 25).attr("y", y - 30)
.attr("width", 50).attr("height", 55)
.attr("rx", 8)
.attr("fill", fill).attr("stroke", stroke)
.attr("stroke-width", 2);
svg.append("text")
.attr("x", x).attr("y", y + 5)
.attr("text-anchor", "middle")
.attr("font-size", "32px")
.attr("font-weight", "bold")
.text(s[i]);
svg.append("text")
.attr("x", x).attr("y", y + 40)
.attr("text-anchor", "middle")
.attr("font-size", "12px")
.attr("fill", "#666")
.text(i);
}
// Current pointer
if (idx < s.length) {
svg.append("text")
.attr("x", startX + idx * charWidth + charWidth / 2)
.attr("y", 55)
.attr("text-anchor", "middle")
.attr("font-size", "16px")
.attr("fill", "#f57c00")
.text("▼");
}
// Range visualization
const rangeY = 220;
const rangeWidth = 300;
const rangeX = (width - rangeWidth) / 2;
const scale = rangeWidth / 8; // -2 to 6
svg.append("text")
.attr("x", width / 2).attr("y", 190)
.attr("text-anchor", "middle")
.attr("font-weight", "bold")
.text("Possible Open Paren Count Range");
// Axis
svg.append("line")
.attr("x1", rangeX).attr("y1", rangeY)
.attr("x2", rangeX + rangeWidth).attr("y2", rangeY)
.attr("stroke", "#333").attr("stroke-width", 2);
for (let i = -2; i <= 6; i++) {
const x = rangeX + (i + 2) * scale;
svg.append("line")
.attr("x1", x).attr("y1", rangeY - 5)
.attr("x2", x).attr("y2", rangeY + 5)
.attr("stroke", "#333");
svg.append("text")
.attr("x", x).attr("y", rangeY + 20)
.attr("text-anchor", "middle")
.attr("font-size", "12px")
.text(i);
}
// Range bar
const minX = rangeX + (Math.max(minOpen, -2) + 2) * scale;
const maxX = rangeX + (Math.min(maxOpen, 6) + 2) * scale;
if (maxOpen >= 0 && minOpen <= 6) {
svg.append("rect")
.attr("x", minX).attr("y", rangeY - 15)
.attr("width", Math.max(0, maxX - minX + 10))
.attr("height", 30)
.attr("rx", 5)
.attr("fill", "#c8e6c9").attr("stroke", "#4caf50")
.attr("opacity", 0.7);
// Min marker
svg.append("circle")
.attr("cx", minX).attr("cy", rangeY)
.attr("r", 8)
.attr("fill", "#4caf50");
svg.append("text")
.attr("x", minX).attr("y", rangeY - 25)
.attr("text-anchor", "middle")
.attr("font-size", "12px")
.attr("font-weight", "bold")
.text(`min=${minOpen}`);
// Max marker
svg.append("circle")
.attr("cx", maxX).attr("cy", rangeY)
.attr("r", 8)
.attr("fill", "#1976d2");
svg.append("text")
.attr("x", maxX).attr("y", rangeY + 40)
.attr("text-anchor", "middle")
.attr("font-size", "12px")
.attr("font-weight", "bold")
.text(`max=${maxOpen}`);
}
// Zero line
const zeroX = rangeX + 2 * scale;
svg.append("line")
.attr("x1", zeroX).attr("y1", rangeY - 25)
.attr("x2", zeroX).attr("y2", rangeY + 25)
.attr("stroke", "#e53935")
.attr("stroke-width", 2)
.attr("stroke-dasharray", "5,5");
// Explanation
svg.append("text")
.attr("x", 50).attr("y", 300)
.attr("font-size", "12px")
.text("'(' → min++, max++");
svg.append("text")
.attr("x", 50).attr("y", 320)
.attr("font-size", "12px")
.text("')' → min--, max--");
svg.append("text")
.attr("x", 50).attr("y", 340)
.attr("font-size", "12px")
.text("'*' → min-- (as ')'), max++ (as '(')");
// Result
if (isValid !== null) {
svg.append("rect")
.attr("x", width - 160).attr("y", height - 80)
.attr("width", 150).attr("height", 50)
.attr("rx", 10)
.attr("fill", isValid ? "#c8e6c9" : "#ffcdd2")
.attr("stroke", isValid ? "#4caf50" : "#e53935");
svg.append("text")
.attr("x", width - 85).attr("y", height - 48)
.attr("text-anchor", "middle")
.attr("font-size", "18px")
.attr("font-weight", "bold")
.text(isValid ? "✓ Valid!" : "✗ Invalid!");
}
}
function step() {
if (isValid !== null) {
draw();
return false;
}
if (idx >= s.length) {
isValid = minOpen === 0;
document.getElementById("resultDisplay").textContent =
isValid ? "Yes ✓" : "No ✗";
document.getElementById("status").textContent =
isValid ? `Valid! min_open = 0 at end.` :
`Invalid! min_open = ${minOpen} ≠ 0`;
draw();
return false;
}
const c = s[idx];
let explanation = "";
if (c === '(') {
minOpen++;
maxOpen++;
explanation = `'(' → min=${minOpen}, max=${maxOpen}`;
} else if (c === ')') {
minOpen--;
maxOpen--;
explanation = `')' → min=${minOpen}, max=${maxOpen}`;
} else { // '*'
minOpen--;
maxOpen++;
explanation = `'*' → min=${minOpen} (as ')'), max=${maxOpen} (as '(')`;
}
if (maxOpen < 0) {
isValid = false;
document.getElementById("resultDisplay").textContent = "No ✗";
document.getElementById("status").textContent =
`Invalid! max_open < 0 means too many ')'`;
draw();
return false;
}
minOpen = Math.max(minOpen, 0);
document.getElementById("rangeDisplay").textContent =
`(${minOpen}, ${maxOpen})`;
document.getElementById("status").textContent = explanation;
idx++;
draw();
return idx < s.length;
}
function reset() {
idx = 0;
minOpen = 0;
maxOpen = 0;
isValid = null;
autoRunning = false;
if (autoTimer) clearInterval(autoTimer);
document.getElementById("rangeDisplay").textContent = "(0, 0)";
document.getElementById("resultDisplay").textContent = "-";
document.getElementById("status").textContent =
'Click "Step" to validate string';
document.getElementById("autoBtn").textContent = "Auto Run";
draw();
}
function autoRun() {
if (autoRunning) {
autoRunning = false;
clearInterval(autoTimer);
document.getElementById("autoBtn").textContent = "Auto Run";
} else {
autoRunning = true;
document.getElementById("autoBtn").textContent = "Pause";
const speed = 2100 - document.getElementById("speed").value;
autoTimer = setInterval(() => {
if (!step()) {
autoRunning = false;
clearInterval(autoTimer);
document.getElementById("autoBtn").textContent = "Auto Run";
}
}, speed);
}
}
document.getElementById("stepBtn").addEventListener("click", step);
document.getElementById("autoBtn").addEventListener("click", autoRun);
document.getElementById("resetBtn").addEventListener("click", reset);
draw();
</script>
</body>
</html>