Improvement

Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>

Author: begeekmyfriend

0042_trapping_rain_water/trap_water.c

@@ -35,22 +35,18 @@ static int trap(int* height, int heightSize)
     int res = 0;
     int l = 0, lmax = 0;
     int r = heightSize - 1, rmax = 0;
+
     while (l < r) {
-        if (height[l] < height[r]) {
-            /* Only lmax is needed for lmax < rmax here */
-            if (height[l] > lmax) {
-                lmax = height[l];
-            } else {
-                res += lmax - height[l];
-            }
+        /* lmax is the highest in height[0...l] and
+         * rmax is the highest in height[r...size - 1]
+         */
+        lmax = height[l] > lmax ? height[l] : lmax;
+        rmax = height[r] > rmax ? height[r] : rmax;
+        if (lmax < rmax) {
+            res += lmax - height[l];
             l++;
         } else {
-            /* Only rmax is needed for rmax < lmax here */
-            if (height[r] > rmax) {
-                rmax = height[r];
-            } else {
-                res += rmax - height[r];
-            }
+            res += rmax - height[r];
             r--;
         }
     }

0042_trapping_rain_water/trap_water.cc

@@ -9,25 +9,20 @@ class Solution {
          * water level of the position would be determined by the opposite side.
          */
         int res = 0;
-        int left = 0, left_max = 0;
-        int right = height.size() - 1, right_max = 0;
-        while (left < right) {
-            if (height[left] < height[right]) {
-                /* Only lmax is needed for lmax < rmax here */
-                if (height[left] > left_max) {
-                    left_max = height[left];
-                } else {
-                    res += left_max - height[left];
-                }
-                left++;
+        int l = 0, l_max = 0;
+        int r = height.size() - 1, r_max = 0;
+
+        while (l < r) {
+            // lmax is the highest in height[0...l] and
+            // rmax is the highest in height[r...size - 1]
+            l_max = max(height[l], l_max);
+            r_max = max(height[r], r_max);
+            if (l_max < r_max) {
+                res += l_max - height[l];
+                l++;
             } else {
-                /* Only rmax is needed for rmax < lmax here */
-                if (height[right] > right_max) {
-                    right_max = height[right];
-                } else {
-                    res += right_max - height[right];
-                }
-                right--;
+                res += r_max - height[r];
+                r--;
             }
         }
 

0045_jump_game_ii/jump_game.c

@@ -1,26 +1,29 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+
 static inline int max(int a, int b)
 {
     return a > b ? a : b;
 }
 
 static int jump(int* nums, int numsSize)
 {
-    int i, lo = 0, hi = 0;
+    int i, right = 0;
     int steps = 0;
-    while (hi < numsSize - 1) {
-        int right = 0;
-        for (i = lo; i <= hi; i++) {
-            /* Assume right > hi for the purpose of the problem */
-            right = max(i + nums[i], right);
+    int fartest = 0;
+    /* 1. Exhaust all the right boundries in the location range of [i...right]
+     * 2. When the search ends up with i==right, update the right boundry as
+     *    the fartest position.
+     * 3. When the search ends up with i==right, it records as one jump step */
+    for (i = 0; i < numsSize; i++) {
+        fartest = max(i + nums[i], fartest);
+        if (i == right) {
+            right = fartest;
+            steps++;
         }
-        /* [lo, hi] is the next location range */
-        lo = hi + 1;
-        hi = right;
-        steps++;
     }
+
     return steps;
 }
 

0045_jump_game_ii/jump_game.cc

@@ -6,17 +6,18 @@ class Solution {
 public:
     int jump(vector<int>& nums) {
         int steps = 0;
-        int lo = 0, hi = 0;
-        while (hi < nums.size() - 1) {
-            int right = 0;
-            for (int i = lo; i <= hi; i++) {
-                // right > hi for nums[i] > 0 
-                right = max(i + nums[i], right);
+        int right = 0;
+        int farthest = 0;
+        // 1. Exhaust all the right boundries in the location range of [i...right]
+        // 2. When the search ends up with i==right, update the right boundry as
+        //    the fartest position.
+        // 3. When the search ends up with i==right, it records as one jump step */
+        for (int i = 0; i < nums.size() - 1; i++) {
+            fartest = max(i + nums[i], fartest);
+            for (i == right) {
+                right = fartest;
+                steps++;
             }
-            // [lo, hi] is the next location range 
-            lo = hi + 1;
-            hi = right;
-            steps++;
         }
 
         return steps;

0198_house_robber/robber.c

@@ -14,10 +14,12 @@ static int rob(int* nums, int numsSize)
     int untaken = 0;
     /* Record max profits of nums[0...i] respectively */
     for (i = 0; i < numsSize; i++) {
-        int tmp_taken = taken;
+        int last_taken = taken;
         /* Taken or untaken nums[i] */
+        /* last taken + nums[i] */
         taken = untaken + nums[i];
-        untaken = max(tmp_taken, untaken);
+        /* max(last untaken, last taken) */
+        untaken = max(last_taken, untaken);
     }
 
     return max(taken, untaken);

0198_house_robber/robber.cc

@@ -8,9 +8,11 @@ class Solution {
         int taken = 0;
         int untaken = 0;
         for (int i = 0; i < nums.size(); i++) {
-            int tmp_taken = taken;
+            int last_taken = taken;
+            /* last untaken + nums[i]*/
             taken = untaken + nums[i];
-            untaken = max(untaken, tmp_taken);
+            /* max(last untaken, last taken) */
+            untaken = max(untaken, last_taken);
         }
         return max(taken, untaken);
     }