Merge pull request #2028 from fwqaaq/patch-35

Update 0746.使用最小花费爬楼梯.md

problems/0746.使用最小花费爬楼梯.md

@@ -312,17 +312,30 @@ func min(a, b int) int {
 ```
 
 
-### Javascript 
-```Javascript
-var minCostClimbingStairs = function(cost) {
-    const n = cost.length;
-    const dp = new Array(n + 1);
-    dp[0] = dp[1] = 0;
-    for (let i = 2; i <= n; ++i) {
-        dp[i] = Math.min(dp[i -1] + cost[i - 1], dp[i - 2] + cost[i - 2])
-    }
+### JavaScript 
 
-    return dp[n]
+```JavaScript
+var minCostClimbingStairs = function(cost) {
+  const dp = [0, 0]
+  for (let i = 2; i <= cost.length; ++i) {
+    dp[i] = Math.min(dp[i - 1] + cost[i - 1], dp[i - 2] + cost[i - 2])
+  }
+  return dp[cost.length]
+};
+```
+
+不使用 dp 数组
+
+```JavaScript
+var minCostClimbingStairs = function(cost) {
+  let dpBefore = 0,
+    dpAfter = 0
+    for(let i = 2;i <= cost.length;i++){
+        let dpi = Math.min(dpBefore + cost[i - 2],dpAfter + cost[i - 1])
+        dpBefore = dpAfter
+        dpAfter = dpi
+    }
+    return dpAfter
 };
 ```
 
@@ -330,38 +343,55 @@ var minCostClimbingStairs = function(cost) {
 
 ```typescript
 function minCostClimbingStairs(cost: number[]): number {
-    /**
-        dp[i]: 走到第i阶需要花费的最少金钱
-        dp[0]: 0;
-        dp[1]: 0;
-        ...
-        dp[i]: min(dp[i - 1] + cost[i - 1], dp[i - 2] + cost[i - 2]);
-     */
-    const dp = [];
-    const length = cost.length;
-    dp[0] = 0;
-    dp[1] = 0;
-    for (let i = 2; i <= length; i++) {
-        dp[i] = Math.min(dp[i - 1] + cost[i - 1], dp[i - 2] + cost[i - 2]);
+  const dp = [0, 0]
+  for (let i = 2; i <= cost.length; i++) {
+    dp[i] = Math.min(dp[i - 1] + cost[i - 1], dp[i - 2] + cost[i - 2])
   }
-    return dp[length];
-};
+  return dp[cost.length]
+}
+```
+
+不使用 dp 数组
+
+```typescript
+function minCostClimbingStairs(cost: number[]): number {
+  let dpBefore = 0,
+    dpAfter = 0
+  for (let i = 2; i <= cost.length; i++) {
+    let dpi = Math.min(dpBefore + cost[i - 2], dpAfter + cost[i - 1])
+    dpBefore = dpAfter
+    dpAfter = dpi
+  }
+  return dpAfter
+}
 ```
 
 ### Rust
 
 ```Rust
-use std::cmp::min;
 impl Solution {
     pub fn min_cost_climbing_stairs(cost: Vec<i32>) -> i32 {
-        let len = cost.len();
-        let mut dp = vec![0; len];
-        dp[0] = cost[0];
-        dp[1] = cost[1];
-        for i in 2..len {
-            dp[i] = min(dp[i-1], dp[i-2]) + cost[i];
+        let mut dp = vec![0; cost.len() + 1];
+        for i in 2..=cost.len() {
+            dp[i] = (dp[i - 1] + cost[i - 1]).min(dp[i - 2] + cost[i - 2]);
         }
-        min(dp[len-1], dp[len-2])
+        dp[cost.len()]
+    }
+}
+```
+
+不使用 dp 数组
+
+```rust
+impl Solution {
+    pub fn min_cost_climbing_stairs(cost: Vec<i32>) -> i32 {
+        let (mut dp_before, mut dp_after) = (0, 0);
+        for i in 2..=cost.len() {
+            let dpi = (dp_before + cost[i - 2]).min(dp_after + cost[i - 1]);
+            dp_before = dp_after;
+            dp_after = dpi;
+        }
+        dp_after
     }
 }
 ```
@@ -369,18 +399,29 @@ impl Solution {
 ### C
 
 ```c
-int minCostClimbingStairs(int* cost, int costSize){
-    //开辟dp数组，大小为costSize
-    int *dp = (int *)malloc(sizeof(int) * costSize);
-    //初始化dp[0] = cost[0], dp[1] = cost[1]
-    dp[0] = cost[0], dp[1] = cost[1];
-
-    int i;
-    for(i = 2; i < costSize; ++i) {
-        dp[i] = (dp[i-1] < dp[i-2] ? dp[i-1] : dp[i-2]) + cost[i];
+#include <math.h>
+int minCostClimbingStairs(int *cost, int costSize) {
+  int dp[costSize + 1];
+  dp[0] = dp[1] = 0;
+  for (int i = 2; i <= costSize; i++) {
+    dp[i] = fmin(dp[i - 2] + cost[i - 2], dp[i - 1] + cost[i - 1]);
   }
-    //选出倒数2层楼梯中较小的
-    return dp[i-1] < dp[i-2] ? dp[i-1] : dp[i-2];
+  return dp[costSize];
+}
+```
+
+不使用 dp 数组
+
+```c
+#include <math.h>
+int minCostClimbingStairs(int *cost, int costSize) {
+  int dpBefore = 0, dpAfter = 0;
+  for (int i = 2; i <= costSize; i++) {
+    int dpi = fmin(dpBefore + cost[i - 2], dpAfter + cost[i - 1]);
+    dpBefore = dpAfter;
+    dpAfter = dpi;
+  }
+  return dpAfter;
 }
 ```