添加 0134. 加油站.md C语言贪心解法方法二

problems/0134.加油站.md

@@ -341,6 +341,7 @@ var canCompleteCircuit = function(gas, cost) {
 ```
 
 ### C 
+贪心算法：方法一
 ```c
 int canCompleteCircuit(int* gas, int gasSize, int* cost, int costSize){
     int curSum = 0;
@@ -370,5 +371,36 @@ int canCompleteCircuit(int* gas, int gasSize, int* cost, int costSize){
 }
 ```
 
+贪心算法：方法二
+```c
+int canCompleteCircuit(int* gas, int gasSize, int* cost, int costSize){
+    int curSum = 0;
+    int totalSum = 0;
+    int start = 0;
+
+    int i;
+    for(i = 0; i < gasSize; ++i) {
+        // 当前i站中加油量与耗油量的差
+        int diff = gas[i] - cost[i];
+
+        curSum += diff;
+        totalSum += diff;
+
+        // 若0到i的加油量都为负，则开始位置应为i+1
+        if(curSum < 0) {
+            curSum = 0;
+            // 当i + 1 == gasSize时，totalSum < 0（此时i为gasSize - 1)，油车不可能返回原点
+            start = i + 1;
+        }
+    }
+
+    // 若总和小于0，加油车无论如何都无法返回原点。返回-1
+    if(totalSum < 0)
+        return -1;
+
+    return start;
+}
+```
+
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