From 91d01d610c4c8e75b8d2789240f43a52bf8fe378 Mon Sep 17 00:00:00 2001
From: jerryfishcode <91447694+jerryfishcode@users.noreply.github.com>
Date: Tue, 28 Sep 2021 00:28:04 +0800
Subject: [PATCH] =?UTF-8?q?=E6=96=B0=E5=A2=9E42.=20=E6=8E=A5=E9=9B=A8?=
 =?UTF-8?q?=E6=B0=B4=20JavaScript=E7=89=88=E6=9C=AC?=
MIME-Version: 1.0
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---
 problems/0042.接雨水.md | 99 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)

diff --git a/problems/0042.接雨水.md b/problems/0042.接雨水.md
index 16c788eb..5326dd7f 100644
--- a/problems/0042.接雨水.md
+++ b/problems/0042.接雨水.md
@@ -534,6 +534,105 @@ class Solution:
 Go:
 
 JavaScript:
+```javascript
+//双指针
+var trap = function(height) {
+    const len = height.length;
+    let sum = 0;
+    for(let i = 0; i < len; i++){
+        // 第一个柱子和最后一个柱子不接雨水
+        if(i == 0 || i == len - 1) continue;
+        let rHeight = height[i]; // 记录右边柱子的最高高度
+        let lHeight = height[i]; // 记录左边柱子的最高高度
+        for(let r = i + 1; r < len; r++){
+            if(height[r] > rHeight) rHeight = height[r];
+        }
+        for(let l = i - 1; l >= 0; l--){
+            if(height[l] > lHeight) lHeight = height[l];
+        }
+        let h = Math.min(lHeight, rHeight) - height[i];
+        if(h > 0) sum += h;
+    }
+    return sum;
+};
+
+//动态规划
+var trap = function(height) {
+    const len = height.length;
+    if(len <= 2) return 0;
+    const maxLeft = new Array(len).fill(0);
+    const maxRight = new Array(len).fill(0);
+    // 记录每个柱子左边柱子最大高度
+    maxLeft[0] = height[0];
+    for(let i = 1; i < len; i++){
+        maxLeft[i] = Math.max(height[i], maxLeft[i - 1]);
+    }
+    // 记录每个柱子右边柱子最大高度
+    maxRight[len - 1] = height[len - 1];
+    for(let i = len - 2; i >= 0; i--){
+        maxRight[i] = Math.max(height[i], maxRight[i + 1]);
+    }
+    // 求和
+    let sum = 0;
+    for(let i = 0; i < len; i++){
+        let count = Math.min(maxLeft[i], maxRight[i]) - height[i];
+        if(count > 0) sum += count;
+    }
+    return sum;
+};
+
+//单调栈 js数组作为栈
+var trap = function(height) {
+    const len = height.length;
+    if(len <= 2) return 0; // 可以不加
+    const st = [];// 存着下标，计算的时候用下标对应的柱子高度
+    st.push(0);
+    let sum = 0;
+    for(let i = 1; i < len; i++){
+        if(height[i] < height[st[st.length - 1]]){ // 情况一
+            st.push(i);
+        }
+        if (height[i] == height[st[st.length - 1]]) {  // 情况二
+            st.pop(); // 其实这一句可以不加，效果是一样的，但处理相同的情况的思路却变了。
+            st.push(i);
+        } else { // 情况三
+            while (st.length !== 0 && height[i] > height[st[st.length - 1]]) { // 注意这里是while
+                let mid = st[st.length - 1];
+                st.pop();
+                if (st.length !== 0) {
+                    let h = Math.min(height[st[st.length - 1]], height[i]) - height[mid];
+                    let w = i - st[st.length - 1] - 1; // 注意减一，只求中间宽度
+                    sum += h * w;
+                }
+            }
+            st.push(i);
+        }
+    }
+    return sum;
+};
+
+//单调栈 简洁版本 只处理情况三
+var trap = function(height) {
+    const len = height.length;
+    if(len <= 2) return 0; // 可以不加
+    const st = [];// 存着下标，计算的时候用下标对应的柱子高度
+    st.push(0);
+    let sum = 0;
+    for(let i = 1; i < len; i++){ // 只处理的情况三，其实是把情况一和情况二融合了
+        while (st.length !== 0 && height[i] > height[st[st.length - 1]]) { // 注意这里是while
+            let mid = st[st.length - 1];
+            st.pop();
+            if (st.length !== 0) {
+                let h = Math.min(height[st[st.length - 1]], height[i]) - height[mid];
+                let w = i - st[st.length - 1] - 1; // 注意减一，只求中间宽度
+                sum += h * w;
+            }
+        }
+        st.push(i);
+    }
+    return sum;
+};
+```
 
 C: