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LeetCode-112-Path-Sum.java
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LeetCode-112-Path-Sum.java
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/*
LeetCode: https://leetcode.com/problems/path-sum/
LintCode: http://www.lintcode.com/problem/path-sum/
JiuZhang: http://www.jiuzhang.com/solutions/path-sum/
ProgramCreek: http://www.programcreek.com/2013/01/leetcode-path-sum/
Analysis:
1.DFS
2.BFS
level order traversal, and find sum to the leaf
*/
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
// 1. DFS
// public boolean hasPathSum(TreeNode root, int sum) {
// if(root == null) return false;
// return DFS(root, sum, root.val);
// }
// private boolean DFS(TreeNode root, int sum, int curr){
// if(root.left == null && root.right == null && sum == curr){
// return true;
// }
// boolean left = false;
// if(root.left != null) left = DFS(root.left, sum, curr + root.left.val);
// boolean right = false;
// if(root.right != null) right = DFS(root.right, sum, curr + root.right.val);
// return left || right;
// }
// 2.A simpler DFS
public boolean hasPathSum(TreeNode root, int sum) {
if(root == null) return false;
if(root.left == null && root.right == null && root.val == sum) return true;
return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
}
// 3.BFS
}
class Solution {
// 1.DFS
// public boolean hasPathSum(TreeNode root, int sum) {
// if (root == null) return false;
// return hasPathSum(root, sum, 0);
// }
// private boolean hasPathSum(TreeNode root, int target, int preSum) {
// // find leaf
// if (root.left == null && root.right == null) {
// if (root.val + preSum == target) return true;
// else return false;
// }
// if (root.left == null) return hasPathSum(root.right, target, preSum + root.val);
// if (root.right == null) return hasPathSum(root.left, target, preSum + root.val);
// return hasPathSum(root.left, target, preSum + root.val) || hasPathSum(root.right, target, preSum + root.val);
// }
// 2.DFS(easier one)
// public boolean hasPathSum(TreeNode root, int sum) {
// if (root == null) return false;
// if (root.left == null && root.right == null && root.val == sum) return true;
// return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
// }
// 3.BFS (level order traversal, and find sum to the leaf)
public boolean hasPathSum(TreeNode root, int sum) {
if (root == null) return false;
Queue<TreeNode> queue = new LinkedList<>();
Queue<Integer> sumList = new LinkedList<>();
queue.add(root);
sumList.add(0);
while(!queue.isEmpty()) {
// process one level
int size = queue.size();
for (int i = 0; i < size; i++) {
TreeNode curr = queue.poll();
int val = sumList.poll();
if (curr.left == null && curr.right == null && (val + curr.val) == sum) return true;
if (curr.left != null) {
queue.add(curr.left);
sumList.add(val + curr.val);
}
if (curr.right != null) {
queue.add(curr.right);
sumList.add(val + curr.val);
}
}
}
return false;
}
}